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/* Copyright (C) 2004-2021 Free Software Foundation, Inc.
This file is part of the GNU C Library.
Contributed by Ulrich Drepper <drepper@redhat.com>, 2004.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
#include <errno.h>
#include <netdb.h>
#include <resolv.h>
#include <stdlib.h>
#include <stdint.h>
#include <arpa/nameser.h>
#include <nsswitch.h>
#include <resolv/resolv_context.h>
#include <resolv/resolv-internal.h>
NSS_DECLARE_MODULE_FUNCTIONS (dns)
#if PACKETSZ > 65536
# define MAXPACKET PACKETSZ
#else
# define MAXPACKET 65536
#endif
/* We need this time later. */
typedef union querybuf
{
HEADER hdr;
unsigned char buf[MAXPACKET];
} querybuf;
static const short int qtypes[] = { ns_t_a, ns_t_aaaa };
#define nqtypes (sizeof (qtypes) / sizeof (qtypes[0]))
enum nss_status
_nss_dns_getcanonname_r (const char *name, char *buffer, size_t buflen,
char **result,int *errnop, int *h_errnop)
{
/* Just an alibi buffer, res_nquery will allocate a real buffer for
us. */
unsigned char buf[20];
union
{
querybuf *buf;
unsigned char *ptr;
} ansp = { .ptr = buf };
enum nss_status status = NSS_STATUS_UNAVAIL;
struct resolv_context *ctx = __resolv_context_get ();
if (ctx == NULL)
{
*errnop = errno;
*h_errnop = NETDB_INTERNAL;
return NSS_STATUS_UNAVAIL;
}
for (int i = 0; i < nqtypes; ++i)
{
int r = __res_context_query (ctx, name, ns_c_in, qtypes[i],
buf, sizeof (buf), &ansp.ptr, NULL, NULL,
NULL, NULL);
if (r > 0)
{
/* We need to decode the response. Just one question record.
And if we got no answers we bail out, too. */
if (ansp.buf->hdr.qdcount != htons (1))
continue;
/* Number of answers. */
unsigned int ancount = ntohs (ansp.buf->hdr.ancount);
/* Beginning and end of the buffer with query, answer, and the
rest. */
unsigned char *ptr = &ansp.buf->buf[sizeof (HEADER)];
unsigned char *endptr = ansp.ptr + r;
/* Skip over the query. This is the name, type, and class. */
int s = __dn_skipname (ptr, endptr);
if (s < 0)
{
unavail:
status = NSS_STATUS_UNAVAIL;
break;
}
/* Skip over the name and the two 16-bit values containing type
and class. */
ptr += s + 2 * sizeof (uint16_t);
while (ancount-- > 0)
{
/* Now the reply. First again the name from the query,
then type, class, TTL, and the length of the RDATA.
We remember the name start. */
unsigned char *namestart = ptr;
s = __dn_skipname (ptr, endptr);
if (s < 0)
goto unavail;
ptr += s;
/* Check that there are enough bytes for the RR
metadata. */
if (endptr - ptr < 10)
goto unavail;
/* Check whether type and class match. */
uint_fast16_t type;
NS_GET16 (type, ptr);
if (type == qtypes[i])
{
/* We found the record. */
s = __libc_dn_expand (ansp.buf->buf, endptr, namestart,
buffer, buflen);
if (s < 0)
{
if (errno != EMSGSIZE)
goto unavail;
/* The buffer is too small. */
*errnop = ERANGE;
status = NSS_STATUS_TRYAGAIN;
h_errno = NETDB_INTERNAL;
}
else
{
/* Success. */
*result = buffer;
status = NSS_STATUS_SUCCESS;
}
goto out;
}
if (type != ns_t_cname)
goto unavail;
uint16_t rrclass;
NS_GET16 (rrclass, ptr);
if (rrclass != ns_c_in)
goto unavail;
/* Skip over TTL. */
ptr += sizeof (uint32_t);
/* Skip over RDATA length and RDATA itself. */
uint16_t rdatalen;
NS_GET16 (rdatalen, ptr);
/* Not enough room for RDATA. */
if (endptr - ptr < rdatalen)
goto unavail;
ptr += rdatalen;
}
}
/* Restore original buffer before retry. */
if (ansp.ptr != buf)
{
free (ansp.ptr);
ansp.ptr = buf;
}
}
out:
*h_errnop = h_errno;
if (ansp.ptr != buf)
free (ansp.ptr);
__resolv_context_put (ctx);
return status;
}
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